This invention relates to a support aligning fixture, and more particularly to a fixture for aligning supports incorporated in a vacuum glass envelope which is formed by joining two glass substrates to each other and evacuated to a vacuum.
In general, a fluorescent display device includes a vacuum envelope in which an electron emission source for emitting electrons in a vacuum atmosphere and a luminous element such as a phosphor excited by the emitted electrons for luminescence are arranged. The vacuum envelope is typically made of glass into a vacuum or sealed structure. More specifically, the vacuum envelope is constructed of a first glass substrate and a second glass substrate arranged in a manner to be spaced at a microinterval from the first glass substrate while being opposite thereto and is provided therein with phosphors for providing a flat display plane and an electron emission source for emitting electrons for luminescence of the phosphors. The envelope thus constructed is then evacuated to a vacuum. Thus, in order to keep the first and second substrates spaced from each other at a predetermined interval irrespective of such evacuation of the envelope to a vacuum, it is typically executed to arrange supports in the form of a pin between the first substrate and the second substrate.
Now, such arrangement will be described hereinafter with reference to FIGS. 6 and 7.
A number of supports 101 in the form of a pin are interposedly arranged between a first substrate 102 and a second substrate 103, although only three such supports are shown in FIGS. 6 and 7 for the sake of brevity. The supports 101 each are typically made of glass fiber into dimensions as small as, for example, about 50 .mu.m in diameter and 200 .mu.m in length.
Such microscopic or microsized supports 101 cause arrangement of the supports 101 between the first substrate 102 and the second substrate 103 by manual operation to be highly difficult or substantially impossible. Thus, a support aligning plate 100 formed with a number of support holes 114 for arranging the supports 101 at predetermined positions on the substrates is used as a fixture for the arrangement as shown in FIG. 6.
More particularly, the supports 101 each are fittedly arranged at a proximal or lower end thereof in each of the support holes 114 of the aligning plate 100 acting as the fixture. The aligning plate 100 is provided on a lower surface thereof with a perforated section 112, through which air is drawn out to raise the supports 101 in the support holes 114. Then, the supports 101 thus raised each are provided on a distal or upper end thereof with a paste 121 for adhesion by transfer printing, through which the supports 101 are adhered or bonded to the first substrate 102 as shown in FIG. 7, resulting in being securely mounted on the first substrate 102.
The description will be further made with reference to FIGS. 8(a) to 8(c). First, a glass fiber material of about 50 .mu.m in diameter for the supports 101 is cut into a length of about 200 .mu.m, to thereby provide the supports 101. The supports 101 thus cut each are cleaned and then positioned with respect to the first substrate 102 by means of a fixture 110. The fixture 101 is formed into a box-like shape as shown in FIGS. 8(a) to 8(c) and includes an aligning plate 111 formed with support holes 114 for raising the supports 101 therein, a perforated section 112 made of a perforated material and arranged under the aligning plate 111, and an evacuation section 113 through which an interior of the fixture 110 is evacuated.
Positions on the aligning plate 111 at which the support holes 114 are formed are determined so as to correspond to positions on the first substrate 102 on which the supports 101 are arranged.
In the fixture 110 thus constructed, the evacuation section 113 is connected to a vacuum pump (not shown). Then, the supports 101 are spread over the aligning plate 111 of the fixture 110 while evacuating the interior of the fixture 110, so that air drawn out through the support holes 114 is permitted to pass through the evacuation section 113. This results in the supports 101 being introduced into the support holes 114 formed into a diameter larger than that of the supports 101, to thereby be raised in the support holes by suction as shown in FIG. 8(a).
Then, a glass plate 120 to which a paste 121 to be transferred is applied is positioned above the fixture 110 as shown in FIG. 8(b) and then contacted with the supports 101, resulting in the paste 121 being transferred from the glass plate 120 to an upper end surface of the supports 101 held on the fixture 110, as shown in FIG. 8(c).
Subsequently, as shown in FIG. 8(c), the first substrate 102 is put on the fixture 110 on which the supports 101 having the paste 121 transferred thereto are held while being aligned with the fixture 110, so that the supports 101 are adhered at one end surface thereof to the first substrate 102. Thus, adhesive force of the paste 121 permits the supports 101 to be transferred to the substrate 102.
The paste 121 mainly consists of seal glass of a low softening point having lead oxide contained therein in order to permit the paste 121 to have a coefficient of thermal expansion approaching to that of the first substrate 102 made of glass. The paste 121 may be mixed with a solvent or the like, to thereby be provided with stickiness, as required. Then, the second substrate 103 is arranged opposite to the first substrate 102 which is mounted thereon with the supports 101 by welding in a manner to be spaced from each other at predetermined intervals, to thereby form a glass envelope. The envelope thus provided is then evacuated to a vacuum, so that a vacuum glass envelope in which the supports 101 are pressedly interposed between the first substrate 102 and the second substrate 103 to which an atmospheric pressure is applied is provided. A space between the first substrate 102 and the second substrate 103 is sealedly closed at a periphery thereof with a seal material (not shown).
Also, the conventional envelope may be so constructed that the paste is deposited on the other or lower end surface of the supports 101 as well by transfer printing. Then, the first and second substrates 102 and 103 are aligned with each other and then heated in a sealing oven. This permits the transferred paste to be melted, to thereby bond the other end surface of the supports 101 to the second substrate 103 through the paste, resulting in the vacuum glass envelope being provided wherein the supports 101 are fixed at both ends thereof to the substrates 102 and 103. The supports 101 may be arranged in a manner to be spaced from each other at intervals of about 2 to 5 mm.
Fitting of the supports 101 in the support holes 114 of the aligning plate 111 thus carried out is shown in FIG. 9. The conventional envelope, as shown in FIG. 9, causes the supports 101 to be arranged in the support holes 114 while being inclined with respect to the support holes 114, resulting in misregistration often occurring therebetween. This is due to a gap of an excessive size defined between the support 101 and the support hole 114 in which the support 101 is fitted. More particularly, the support holes 114 each are generally formed into a diameter of about 53 .mu.m so as to define a gap of a slight size between the support 101 and the support hole 114 in order to prevent hang-up of the support 101 in the support hole 114 due to friction therebetween. The support 101 is generally formed so as to have a tolerance of .+-.3 .mu.m, whereas the support hole 114 has a tolerance of +5/-0 .mu.m, so that an excessive gap is often undesirably defined between the hole 101 and the support hole 114.
Also, in order that the aligning plate 111 formed with the support holes 114 is prepared with increased accuracy, it is required to restrict a thickness of the aligning plate 111 to a level less than about 70 .mu.m. Unfortunately, this causes the supports 101 to be projected by a distance as large as about 130 .mu.m from the aligning plate 11, resulting in the supports 101 being rendered unstable.
This results in the amount of displacement .delta. of a center of the support 101 from a center of the support hole 114 being increased to about 20 .mu.m or less. Unfortunately, such displacement of the support 101 as large as about 20 .mu.m in an envelope for a fluorescent display device in which picture cells are arranged in a manner to be spaced at pitches of 360 .mu.m and intervals of 80 .mu.m from each other may possibly cause troubles such as deterioration in display of a display section by the supports 101, short-circuiting of internal electrical wirings and the like.
The reason why the conventional envelope fails to increase a thickness of the aligning plate 111 to about 70 .mu.m or more is due to preparation of the aligning plate 111. Now, the manner of manufacturing of the conventional envelope 11 will be described with reference to FIGS. 10(a) to 10(d). First, as shown in FIG. 10(a), a photoresist 132 is coated on a stainless steel plate 131. Then, a glass photographic plate 133 having a mask 134 formed on one surface thereof is arranged on the photoresist 132, followed by irradiation of light onto the photographic plate 133, to thereby expose the photoresist 132 to light, as shown in FIG. 10(b) Then, the photoresist 132 is subject to development, so that only photoresists 135 exposed to light remain on the stainless steel plate 131 as shown in FIG. 10(c). A number of such photoresists 135 are formed on the stainless steel plate 131 while being aligned with positions on which the supports 101 are raisedly arranged.
Then, the stainless steel plate 131 is subject to electroplating using nickel (Ni) as a material to be electroplated, so that a nickel plate 136 may be formed on only the stainless steel plate 131 as shown in FIG. 10(d).
Then, the photoresists 135 are removed, so that regions on the stainless steel plate 131 occupied by the photoresists 135 may permit the nickel plate 136 to be formed with apertures each acting as the support hole 114. Then, the nickel plate 136 is removed from the stainless steel plate 131, resulting in providing the aligning plate 111 formed with a number of the support holes 114.
An increase in thickness of the aligning plate 111 may be attained by increasing a thickness of the photoresist 132 coated on the stainless steel plate 131. Unfortunately, an increase in thickness of the photoresist 132 causes a degree to which light irradiated for exposure is scattered in the photoresist 132 to be increased, leading to a deterioration in accuracy of patterning of the photoresist 132. More specifically, the photoresist 135, as shown in FIG. 10(c), is exposed to light in a manner like a trapezoid in section due to scattering of light irradiated. Thus, an increase in thickness of the aligning plate 111 causes the support holes 114 to be formed while being tapered, leading to a deterioration in accuracy of dimensions thereof.
Such a deterioration in accuracy of dimensions of the support holes 114 and such formation of the tapered support holes 114 in the aligning plate 111 render a diameter of an upper portion of the support holes 114 different from that of a lower portion thereof, so that displacement of the support 101 fitted in each of the support holes 114 from a center of the support hole 114 is further increased as will be noted from FIG. 9. This results in the conventional vacuum glass envelope being unsuitable for a fluorescent display device.
Thus, it will be noted that a thickness of the aligning plate 111 is limited to less than about 70 .mu.m.
In order to solve the problem, the assignee proposed a support aligning fixture constructed as shown in FIG. 11. The support aligning fixture proposed is constructed into a two-layer structure and includes an aligning plate constructed of a first aligning plate member 150 formed into a thickness of about 30 .mu.m and provided with support holes with increased accuracy and a second aligning plate member 151 formed into a thickness of about 90 .mu.m and provided with support holes. The support holes of the second aligning plate member 151 may be formed with reduced accuracy as compared with those of the first aligning plate member 150. The support holes of the second aligning plate member 151 are formed into a diameter larger than that of a diameter of supports 101. Positioning of the supports 101 is carried out by means of the support holes of the first aligning plate member 150. The support aligning fixture thus constructed permits the supports 101 to be supported at a high position in the support hole of the first aligning plate member 150. Also, it improves positional accuracy of the supports 101 or accuracy with which the supports 101 are positioned in the support holes, because the support holes of the first aligning plate member 150 are formed with increased accuracy.
Nevertheless, the support aligning plate shown in FIG. 11 has a disadvantage that operation of fitting the supports 101 in the fixture is rendered difficult or troublesome. More particularly, the tapered support holes 114 formed through the aligning plate 111 shown in FIG. 9 are formed at an upper portion thereof into a diameter of about 60 .mu.m and the supports 101 are formed into an average diameter of about 50 .mu.m, so that a gap as large as about 10 .mu.m may be defined between each of the supports 101 and each of the support holes 114, which is sufficient to facilitate the support filling operation. On the contrary, in the aligning plate of the two-layer structure shown in FIG. 11, the supports 114 are formed at an upper portion thereof into a diameter of 53+3/-0 .mu.m and the supports 101 are formed into an average diameter of about 50 .mu.m, so that a gap therebetween is as small as about 3 to 6 .mu.m.
Also, the fixture shown in FIG. 11 is adapted to be applied to supports of 150 to 300 .mu.m in length. More particularly, a fluorescent display device wherein an anode voltage is set to be about 200 to 600 V is so constructed that intervals between gates and anodes are set to be 150 to 300 .mu.m so as to permit the device to withstand the anode voltage.
In general, luminous efficiency of a phosphor is enhanced with an increase in anode voltage. An increase in anode voltage requires to increase intervals between the gates and the anodes to withstand the anode voltage. For example, setting of the anode voltage at 1000 V requires to increase intervals between the gates and the anodes to 500 .mu.m or more.
Unfortunately, in the fixture of FIG. 11 including the aligning plate of the aligning plate members 150 and 151, the aligning plate has a thickness limited to about 70 .mu.m or less in order to improve accuracy with which the support holes are formed. Thus, the prior art fails to permit the supports of 500 .mu.m in length to be arranged with increased positional accuracy.